Transient electrostatic discharge (ESD) clamps are very effective with respect to ESD protection because they respond quickly to an ESD event and can clamp well. Moreover, they are easily simulated. Two common types of clamps include a CMOS clamp and a bipolar clamp. In a common CMOS clamp design, an active device is used to keep the main clamping transistor off until needed. In a purely bipolar process used to form a bipolar clamp, there is not an effective element to keep the clamp turned off once power is applied since the clamp has to draw power to keep it turned off. This makes it unattractive from total power consumption standpoint. However, a transient bipolar clamp has its advantage because it can respond to transient voltages of a few volts. In addition, the rise time that a bipolar clamp responds to can be tuned by adjusting the resistance and capacitance of the RC network. An issue with transient bipolar clamps is the switching noise produced by circuit operation. The noise could exceed the transient voltage threshold of the clamp causing the ESD clamps to falsely trigger.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a transient clamp with a high trigger voltage to prevent noise transients from falsely triggering the clamp while it is powered up and does not consume the added power that a keep off circuit would require.